Friction Stir Welding assisted by electrical Joule effect

• New concept of FSW assisted by external electrical heat source.
• Temperature raised 200–300 °C with I = 800 A, viscoplasticity increased without affecting metallurgical characteristics.
• Reduce LoP width from 20 to 3 μm under conditions tested.
• Reduces sensitivity of FSW to generate root defects.

This paper presents a variant of Friction Stir Welding (FSW) aiming to minimize or eliminate the root defects that still constitute a major constrain to a wider dissemination of FSW into industrial applications. The concept is based on the use of an external electrical energy source, delivering a high intensity current, passing through a thin layer of material between the back plate and the lower tip of the tool probe. Heat generated by Joule effect improves material viscoplasticity in this region, minimizing the root defects. The concept was validated by analytical and experimental analysis. For the later, a new dedicated tool was designed, manufactured and tested. Numerical simulations were performed to study the electrical current flow pattern and its effect on the material below the probe tip. The potential use of this variant was shown by reducing the size of the weld root defect, even for significant levels of lack of penetration, without affecting overall metallurgical characteristics of the welded joints.

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